In recent years, beams having a so-called top-hat-shaped beam profile (hereinafter simply referred to as a top-hat beam for convenience of explanation) have been drawing attention. A top-hat beam has a beam profile in which the intensity is kept relatively high and uniform within a certain range from the beam center while the intensity is gradually decreased away from the border of the range. Since top-hat beams have a broader range of a substantially uniform energy distribution, application of top-hat beams to, for example, lighting in a spinning-disk confocal microscope or to laser machining devices has been studied.
An example of methods proposed for forming a top-hat beam includes forming a plurality of radiation patterns different in size by using a first optical member and then combining a smaller radiation pattern with a larger radiation pattern that is overlapped around the smaller pattern by using a second optical member (see Patent Literature 1, for example).